| The geological condition of northwest of Hubei are metamorphic rocks,60% of which are consist of schist. The regional tectonics is complex; the fundamental characteristics of schist indicate it is easy to soften. With development of motorway construction in Hubei province, there are some problems in soft schist tunnel construction. Based on the "controlling engineering of motorway in Guzhu Hubei-Tugongling tunnel" project, the deformation of sericite soft schist tunnel and the control technology are analyzed. The tunnel is located in the Shiyan Hubei province. The regional fault, rock joints and fissures, and fold structure are well-developed, and Zhushan fracture is close to the tunnel which leads to the poor stability of tunnel. During the excavation, some problems like large deformation, crack of supporting and collapse are often discovered. This puts off the construction of tunnel and jeopardizes the workers. Therefore it is useful to investigate the mechanical properties and deformation pattern of surrounding rock and put forward some effective control measures.This paper focuses on "deformation behavior and support technology of soft pinal schist tunnel construction". Based on the "controlling engineering of motorway in Guzhu Hubei-Tugongling tunnel" project, several content have been investigated like "deformation mechanism of soft schist tunnel, deformation behavior, and surrounding rock supporting technology" by using "field investigation, laboratory test, creep test, numerical simulation, field monitor measuring". The main works of this research are presented as followed:(1) The engineering geological environment in the study area is detailed investigated. The deformation behavior of tunnel has close relationship with geological environment of tunnel, geometric shapes of tunnel, and excavation methods of tunnel. Landform, formation lithology, geological structure, rock structure, hydrological conditions are the important part of geological environment. Based on the Gucheng to Zhuxi motorway tunnel construction engineering, the above-mentioned information are being investigated, and the relevance between geological and hydrological condition with stability of surrounding rock are being evaluated. Crustal stress is tested to analyze the characteristics of stress field from stress values, coefficient of horizontal pressure, stress orientation these aspects, and to evaluate the surrounding rock stability of tunnel. By using DIPS software, dip or along the strike of joint fissure are analyzed to obtain characteristic of dominant structure plane and schistosity plane. Furthermore, some relative problems which are cause by large deformations of surrounding rocks are analyzed.(2) The surrounding rock of tunnel are typical pinal shale which is Multi-angle development, lower strength, poor consolidation, metamorphic degree of inequality What is more, underground water of tunnel area is abundance which leads to the soften, swell, disintegration of rock. Therefore, there are some close relationship between the deformation of tunnel and the characteristic pinal shale. By using microstructure test (rock slice microscope test, environmental scanning electron microscope test), physical property test (density, gap, mineral analysis wave velocity test), Hydraulic test (water absorptive test), mechanical test (dry uniaxial and triaxial test, creep mechanics test), and acoustic emission test, the microstructure characteristics of pinal shale, physico-mechanical index of pinal shale, and dynamic failure process characteristics in loading procedure of pinal shale are presented. These researches provides scientific basis for analyzing surrounding rock mass deformation, and provides the basic parameters for creep constitutive model and numerical modeling as well.(3) Pinal shale has significant rheological property due to the coupling between the underground water and crustal stress which is shown like long time of surrounding rock deformation and large deformation. Based on the triaxial creep mechanics test, the creep constitutive model and its parameter are analyzed. Furthermore, based on summarizing classic creep models, Burgers model are improved which can define the initial creeping stage, constant speed creeping stage, and accelerate creeping stage of pinal schist. By using least square method, strain-time creep data are fit to obtain the parameters of viscoelastic plastic creep constitutive model. The change pattern of these parameters is expored, and the influence between the moisture content and these parameters is also analyzed.(4) By using ANSYS software, the numerical simulation model of Tugongli tunnel is built. The calculation parameters are obtained by transforming the viscoelastic plastic creep constitutive model parameters into Prony series form. Throughout the numerical simulation, the deformation mechanism of soft schist tunnel, deformation behavior, and change pattern of surrounding rock deformation are analyzed. These can provide theoretical analysis, construction scheme for the tunnel construction.(5) Deformation mechanism of soft schist tunnel are analyzed from surrounding rock deformation influence factor, deformation macroscopic characteristics, deformation mechanism, and the site monitoring measurement these four aspects. The mechanism of large deformation of surrounding rock can be divided into to five parts like lithological characters, Structure characteristics of surrounding rock, geological structure, crustal stress, and underground water by using all kinds of test, theoretical calculation, and numerical analysis method. Some basic information about Tugongling tunnel cracks are investigated like position, length, quantity, dip, width. The finite element software PLAXIS is used to analyze the surrounding rock stress, internal force of lining to reveal failure mechanism and outbreak pattern of silk mica schist cracks. What is more, the phenomenon and mechanism of large deformation of surrounding rock can be revealed by monitoring research like vault crown settlement, peripheral displacement convergence, supporting pressure, axial force of the anchor, and strain of concrete.(6) Preliminary bracing technology in soft schist tunnel is put forward, and the basic principle of deformation control of soft schist tunnel surrounding rock is introduced. Furthermore, supporingt technology of soft schist tunnel is analyzed from construction method support parameter these two aspects. The specific processing measures like temporary support reinforcement, ductule grouting reinforcement, preliminary bracing sprayed concrete, monitoring measurement is used to control the deformation of surrounding rock. The innovation achievements of this paper are presented as follow:(1) By using microstructure test (rock slice microscope test, environmental scanning electron microscope test), physical property test (density, gap, mineral analysis wave velocity test), Hydraulic test (water absorptive test), mechanical test (dry uniaxial and triaxial test, creep mechanics test), and acoustic emission test, the microstructure characteristics of pinal shale, physico-mechanical index of pinal shale, and dynamic failure process characteristics in loading procedure of pinal shale are presented. These researches provides scientific basis for analyzing surrounding rock mass deformation, and provides the basic parameters for creep constitutive model and numerical modeling as well.(2) Based on the triaxial creep mechanics test, the creep constitutive model and its parameter are analyzed. Furthermore, based on summarizing classic creep models, Burgers model are improved which can define the initial creeping stage, constant speed creeping stage, and accelerate creeping stage of pinal schist. Strain-time creep data are fit to obtain the parameters of viscoelastic plastic creep constitutive model. The change pattern of these parameters is expored, and the influence between the moisture content and these parameters is also analyzed.(3) By using ANSYS software, the numerical simulation model of Tugongli tunnel is built. The calculation parameters are obtained by transforming the viscoelastic plastic creep constitutive model parameters into Prony series form. Throughout the numerical simulation, the deformation mechanism of soft schist tunnel, deformation behavior, and change pattern of surrounding rock deformation are analyzed. These can provide theoretical analysis, construction scheme for the tunnel construction.(4) Some basic information about Tugongling tunnel cracks are investigated like position, length, quantity, dip, width. What is more, finite element software PLAXIS is used to analyze the surrounding rock stress, internal force of lining to reveal failure mechanism and outbreak pattern of silk mica schist cracks. Based on the monitoring measurement like vault crown settlement, peripheral displacement convergence, supporting pressure, axial force of the anchor, and strain of concrete.(5) Furthermore, supporingt technology of soft schist tunnel is analyzed from construction method support parameter these two aspects. The specific processing measures like temporary support reinforcement, ductule grouting reinforcement, preliminary bracing sprayed concrete, monitoring measurement is used to Control the deformation of surrounding rock. |
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